This invention relates to lightweight, high strength, container/transporter systems suitable for handling a wide variety of bulk materials or fluids. The present invention is particularly suited for incorporation into a novel line of dump trucks, dump trailers, refuse collection and/or transportation vehicles, railroad cars and the like. It has important benefits in cost reduction and energy resource conservation, and significant benefits in reduction of environmental degradation
When both energy costs and labor costs were but a fraction of today's costs, manufacturers typically simply built rectangular boxes to receive, transport and unload such materials. Although it was known that flat plates could resist less stress than similar plates formed into any of a great variety of shapes, early manufacturers simply added enough reinforcing members at enough locations to permit the flat plate, rectangular box designs to withstand the loads of the intended applications. The resulting product was extremely heavy and unnecessarily wasteful of both material and energy resources, both in the initial manufacture and in subsequent utilization.
With the rising real costs of energy for transportation, more and more manufacturers began to look for more efficient receiving, transporting and unloading systems. Some resorted to cutting steel railroad tank cars in half, but while this expedient typically permitted the use of fewer reinforcement members, the final product was still unnecessarily heavy and consumptive of expensive energy resources. Others resorted to a simple substitution of lighter weight materials in the old rectangular box, heavily reinforced designs. Still others looked for ways to reduce overall weight while maintaining the required strength through new designs.
Exemplary of the latter is the design of George Logue as shown in U.S. Pat. No. 3,897,972 issued 5 Aug. 1975. Logue discloses a 45.degree. inclined flange joining the flat sidewalls and the flat floor and a plethora of longitudinal supports and cross buttresses. The weight-saving feature of Logue is the provision of tapered rather than full-sectioned side buttresses. It will be readily appreciated that the weight saving of the Logue design is slight. Similarly, U.K. Pat. No. 2141077 to John Lasker discloses a flat floor an edge portion of which has been formed at a 45.degree. angle and reinforced by bottom rails. The floor comprises three pieces welded longitudinally and, with the two side pieces, constitutes a four-piece shell.
U.S. Pat. No. 3,844,616 issued 29 Oct. 1984 to Acker discloses a half-elliptical-bottomed dump body formed of sheet metal, presumably steel, and three arcuate sections joined, presumably by welding, to a pair of vertical side walls. The half-ellipse shape is obtained by forming the center arcuate section to a radius of curvature three times the length of the radii of curvature of the "corner" arcuate sections. Acker does not specify whether the three arcuate sections are formed separately and welded longitudinally the length of the body, or are formed in one piece and welded transversely to a plurality of similar shaped sections. In any event, although it is stated as an object of that invention to provide a construction not requiring stiffeners and bolsters, Acker found it necessary to incorporate a bolster on each side, substantially at the center of the shell, which extend from the top rail to almost the bottom of the shell. The absence of reinforcing supports would seem to preclude the use of lightweight metals such as aluminum for all but the shortest of shells.
U.S. Pat. No. 3,583,331 to Mowatt-Larssen and U.S. Pat. No. 4,909,564 to Pfiefer and Homing employ arcuate sections in rail cars and refuse vehicles, respectively, but both appear to employ non-symmetrical sections.
Every material available today has some inherent disadvantages. Materials lighter than steel tend to be harder to work with, more elastic and less rigid, and generally may not be welded so as to maintain the strength of the material across the region of the weld. Aluminum, for example, typically undergoes a reduction in yield and tensile strength in the neighborhood of from 30% to 45% when welded. Also, aluminum has such a high coefficient of elasticity - i.e., tends to "spring back" so much when formed - as to make this material difficult to work with conventionally.
Both steel and aluminum have been used in the construction of "round bottom" containers for dump trucks and trailers. However, due at least in part to the difficulty of forming metal in sections more than about twenty feet or so in length, such prior devices have incorporated multiple sections of plate joined by circumferential welds and, in most instances, reinforced by either partial or full circumferential ribs. Typically illustrative is a dump trailer manufactured by Fruehauf, one of the larger trailer manufacturers in the country; its model DRX-M2-30 may be seen to be comprised of four half-rounded sections welded circumferentially and, even though made of quarter-inch high-strength steel with a yield strength of 100,000 psi, is reinforced with at least partially circumferential ribs at the bottom of each circumferential weld. Further, a massive, fully circumferential rib is seen to reinforce the body very near the midsection and a large, heavy-duty partial frame is utilized from the massive circumferential rib back to the end of the trailer, i.e., for nearly half the length of the trailer. Although only 30 feet in length and 23 cubic yards capacity, the estimated weight of the trailer is some 13,750 lbs. Were aluminum to be substituted for steel in such a design, a similar large circumferential rib would be required to support the circumferential welds joining each section. Since the total weight of vehicle and payload is limited by law, each such large reinforcement member directly reduces the allowable payload, i.e., on a pound-for-pound basis. Further, since cost such vehicles travel at least as far in an unloaded condition as they do loaded, the greater the empty weight, the greater the unnecessary depletion of energy resources.
An aluminum-bodied trailer known in the trade as the `bathtub` design has also been tried heretofore. This design incorporates multiple short sections of aluminum welded circumferentially and supported with multiple circumferential ribs. In cross-section, it has an appearance similar to that of a bathtub, i.e., flat bottom, straight sides, rounded corners. Despite its multiplicity of supporting circumferential ribs, however, and despite having been designed and manufactured by one of the nation's largest and most reputable manufacturers, this design is known for its propensity to break in half upon encountering harmonic loading during transit.
As best as can be determined by applicant, it appears that there is no fully satisfactory, truly lightweight end-dumpable trailer of full length and capable of transporting full loads on the market today, despite the long felt and pressing need therefor.
These and other disadvantages of the prior art are overcome with the present invention, however, and novel and improved techniques and apparatus are accordingly provided herein for more efficiently transporting products and at lower cost.